Looking back on my wkhtmltopdf / Heroku experience, there are several take-aways for me.
First off, I had contacted Heroku technical support for assistance, and got back a quick reply:
Unfortunately we don't support installing additional libraries or binaries to our stacks. The best workaround is to vendor these into your project. You'll need to use 64-bit Linux versions to make them work on Heroku; compiling statically can also help ensure that any dependencies needed are included. Similarly, for gems that depend on external libraries, we recommend compiling the gem statically and vendoring it into your project (which is what it seems you have already tried to do).Kinda makes sense to me: they have to protect their stack. I'm not surprised, just a wee bit disappointed that they don't make something as widespread and generally useful as wkhtmltopdf available as a standard binary. Oh well; they do seem to be looking into a better solution, and they did provide some good information. The link to that project looks like it might be useful in the future.
We realize this is not a trivial task and can be very difficult to get working, and we hope to provide an easier way to do this in the future. Unfortunately we do not have an ETA on when this improved functionality will be available.
If you do wish to try to vendor, or if you have no success with vendoring, your binary, library, or gem, you can use Heroku as your build environment. One of our engineers created a build server that allows you to upload source code, run the compilation step, and then download the resulting binary. You can find this project on Github.
Once I got my app with PDF working, I submitted a documentation update to WickedPDF, which was promptly merged (thanks @unixmonkey). Hopefully that'll provide some assistance to other folks.
One of the problems I had with the various gems that include binary versions of wkhtmltopdf was that they hadn't been updated recently... sometimes in over a year. So I figured that I should be a good citizen and update them with the latest version (0.11.0 rc1 at the time I'm writing this). To that end, I just submitted a pull request for the wkhtmltopdf-heroku gem. It purports to automagically support WidkedPDF, PDFKit, and wisepdf, depending on which one is loaded (I've not tested it myself).
However, when I started looking at the wkhtmltopdf-binary "family" of gems, it was pretty involved: steerio/wkhtmltopdf-binary (the one I originally investigated), is forked from unixmonkey/wkhtmltopdf_binary_gem which in turn is forked from michaelcollas/wkhtmltopdf_binary_gem, which is itself forked from zakird/wkhtmltopdf_binary_gem and who know how many forks there are on side legs...
That's not something I'm inclined to sign up for! And given the simplicity of adding the single binary in my app (now that I know how to do it), I'm inclined to keep it that way and avoid any of those gems entirely. In fact, I'm beginning to come to the conclusion that it may be better in the long run to install things manually for what I'll call "minor" gem functionality [Note to self: come up with better terminology for this situation] such as this one: I know more of what's going on and have more control over the final outcome.
It also reminds me that, while we work hard to DRY up our code, the proliferation of similar gems on the web is anything but DRY.